Gels based on calcium alginate/pillared bentonite: structural characterization and their use as cadmium removal agent

In this work, calcium alginate hydrogels with natural and pillared bentonites (0.5 and 5% w/w) were synthetized in two geometries (disks and beads) and their capacity to adsorb cadmium ion from aqueous media was evaluated. Pillarization effect on bentonite morphology was evidenced by SEM, XRD, LD and BET isotherms. Structure and swelling capacity of hydrogels were determined, showing that hydrogels beads with pillared clays presented the higher ability to retain water. Regarding cadmium adsorption capacity, the effect of pH media (3, 5 and 7), the contact time (0 to 320 min.) and the initial cadmium ion concentration (6 to 42 mg/L) were studied employing hydrogel beads. Regardless bentonite type and concentration, the optimal pH cadmium adsorption was 7, reaching the highest adsorption capacity (93%) for hydrogel with 0.5% natural bentonite. Besides, the equilibrium adsorption time was reached at 120 min for all studied hydrogels and experimental data fitted with a pseudo-second order kinetic model.